Miniature refrigeration device



Oct. 27, 1959 A. PAsTUHov ET AL 2,909,908

MINIATURE REFRIGERATION DEVICE Filed Nov. 6, 1956 5 Sheets-Sheet 1HRG/15 /N -l- Axas PAST Hov FRANK J. mMmf/mm; v

Oct. 27, 1959 A. PAsTuHov ETAL 2,909,908

MINIATURE REFRIGEEATION DEVICE Filed Nov. 6, 1956 5 Sheets-Sheet 2 I 2ol 4a 'l A2645 our 7/ IFI/'54 INVENTORS ALEXIS PAsTu H By FQAMK J.ZIMMEEM Oct. 27, 1959 A. PAsTuHov Erm.- 2,909,908

MINIATURE REFRIGERATION DEVICE Filed Nov. 6, 1956 5 Sheets-Sheet 3 HRGAS M/ /T i IWW nl; T. N

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INVENTORS `ALEXISv PAsTu Hav BY FQANK J. ZIMHEKMANN rlTl lll/lll//l/l//ll/ 0d 27 1959 A. PIIssrul-iovv I-:TAL 2,909,908

MINIATURE REFRIGERAIION' DEVICE JNIGNTORS ALEXIS PASTUHOV FRANKJ.ZIMMEMMI QM//Zm y A. 'PASTUHOV ET Al.

MINIATURE REFRIGERATION DEVICE oct. 27, 1959 5 Sheets-Sheet 5 Filed Nov.6, 1956 FIG 6 JNVENTORS ALDUS, PASTUHOV 2,909,908 l MINIATUREREFRIGERATION DEVICE Application November 6, 1956, Serial No. 620,676 sGrams. (ci. ca -222) This invention relates to miniature refrigerationdevices utilizing the Joule-Thomson effect, which are especially usefulin providing intense cooling of small surfaces or areas such as those ofsmall energy-detecting units.

The sensitivity of some types of energy-detecting units, such as thoseused for detecting infra-red or heat radiation, is increasedconsiderably by cooling the detecting means to very low temperatures.The purpose of this invention is to provide a simple, compact device forcooling the detector means to very low temperatures, which device can beeasily assembled, disassembled, and cleaned, can be simply manufactured,and occupies a minimum of space.

Briefly stated, the device of this invention comprises a tubularheat-exchanger having two concentric thermally f bonded spiralpassageways, with lmeans at one end for admitting high-pressure gas intothe inner passageway, an expansion valve at the other end for expandingthe high pressure gas emerging from the inner passageway and directingit into the outer passageway, wherein it flows in out-of-contactcounter-current heat exchange relation with the incoming high-pressuregas, and means at the inst-mentioned end for removing the outgoinglowpressure gas from the outer passageway. This low-pressure gas iscompressed in a compressor, cooled in an aftercooler, passed through oilfilters vand separators to whatever extent necessary, and Vreturned -tothe highpressure side of the device. Thefaforesaid tubular heatexchanger is surrounded at its`cold end and throughout most of itslength with a Dewar, in which is adetector such as an infrared detectorlcell located adjacent the coldest end of the device. The Dewar isprovidedwith a window arranged to admit radiation to the detector cell,and leads are provided from the cell out through the walls of the Dewarto a conventional measuring device.

The tubular heat-exchanger described above may -also be made with morethan one pair -of concentric spiral passageways, so that lowertemperatures can be'attained by using two or more gases.

The device of this invention canbe used generallyfor providing lowtemperatures at desired points, for example in the cooling of unitsemployed in the detection of infrared or heat radiation. Such unitssocooled provide a passive means for such detection-ie. no radiation isemittedand may be used for example 'in tire detection by placing one ormore of'them in vlocations-wifiere fire might occur and connecting themthrough the aforesaid leads to an alarm associated with the measuringdevice.

United States Patent O fice This invention will now be described inmoredetail in connection with the accompanying drawings, which are to beconsidered illustrative rathery than? limiting, and in which: f

Fig. 1 represents a cross-sectionalview of'afpreferred form of theheat-exchanger device; Figs. 2 and 3 represent cross-sectionalviewsofmodilied forms of the device shown in Fig. 1;

body member 30 firmly iixed thereto;

" sageway formed by 2,909,908 Patented Oct. 27, 1959 Fig. 4 is a View,partly in section, of the heat-exchanger device associated with a Dewarand a detector cell;

Fig. 5 is a flow diagram showing the arrangement for providing thecompressed refrigerating gas to the heatexchanger device; and

Fig. 6 represents a cross-sectional view of a modied form of theheat-exchanger device wherein a second pair of passageways is providedto increase the cooling effect.

The device shown in Fig. l is made up of a central rod 10 provided withspiral threads 12 throughout its length, a cylindrical tube 14 ofheat-conductive metal tting against the apexes of threads 12 andprovided with a spirally-wound strip 16 of heat-conductive metalthermally bonded to tube 14, and an outside cylindrical tube 18surrounding this assembly and close to strip 16. The tube 14 is made soas to t tightly against threads 12 when the device is in operation;hence the gases pass along the spiral channels provided by threads 12and strip 16, and do not by-pass them. When the device is warmed toabout room temperature, the tit is suiiiciently loose to permit readyassembly and disassembly.

Tube 14 is supported by entrance conduit 2d attached to one end thereof,and is provided at the other end with a small block 22 havingtherethrough an oriiice 24. Cooperating with orifice 24 is needle 26mounted on end 23 of tube 18, thereby providing an expansion valve, inthe form of a needle valve. At the other end of tube 1S is this memberand conduit 20 are provided with cooperating threads 32. Gases emergingfrom travel around spiral strip 16 escape into space 34. Skirt 36 isattached in gas-tight relation to `conduit 20; O-ring seal 38 positionedin body member 30 provides a gas-tight seal between member 30 and skirt36. The emerging Vgases pass from space 34 out through exit 40, which isin gas-tight relation with skirt 36, whiletheihigh-pressure gases enterthe device through opening 42 in conduit 20.

The device of Fig. l is assembled by inserting threaded rod 10 intofinned tube 14. Insertion of removal of this rod can be facilitated byusing a wrench inserted in hole 44 in the top of rod 10, which isconveniently inserted and removed with a turning or threadingmotion'rather than straight in or out. vMember 301is then screwedV intoconduit 20 via threads 32, thereby moving skirt 36 down tightlyoverO-ring seal 38. The distance to which member 30 is screwed onto conduit20 determines the distance to which needle 26 moves into orifice 24, andhence the needle valve setting.

12. The expanded gas then passes into space 34 and thence out of thedevice through pipe 40.

In operation, there is sometimes a tendency for deposits nfrom theincoming highpressure gaseous stream to form in, and plug, the threads12, particularly in the coldest part of the length of the threads. Toassist in correcting this ditliculty, the lower threads on rod 10 may bemade deeper and'further apart, thus providing channels ofA largercross-sectional area in the spiral pasthe threads on rod`10. Such anarrangement is indicated in Fig. 2, where the deeper and -further-apartthreads are indicated bythe numeral 1 3,

other' `parts being the same aslike-numbered parts in The arrangementshown in Fig. 3 is functionally like that in Fig. 1, except that theFig. 3 arrangement provides a needle valve setting which is lessaffected by thermal contraction than that in Fig. 1. However, the Fig. 1arrangement is satisfactory for most operations, whereas in the Fig. 3arrangement the amount of metal `at the cold end is larger than issometimes desired.

The device shown in Fig. 3 is provided Vwith rod 10, threads 12 thereon,tube 14, spiral strip 16, and tube 18, as in Fig. 1. At the cold end oftube V14 is attached block 50, having openings 52, orifice 53communicating therewith, and threads 54 which fit like threads on needle56 which is mounted on end 28 of tube 18. Collars 55 prevent needle 56from jamming in orifice 53. At the warm end of the device is head block58 having inlet port 60 and outlet 62 leading from chamber 64 into whichthe low-pressure gas moving along the spirals 16 discharges. O-ring 66,positioned in annular channel member 67 which is fixed to tube 18,provides a fiuidtight seal for chamber 64. The warm end of tube 14 isfixed to head block 58.

The device of Fig. 3 is assembled by first placing rod in tube 14, asdescribed for Fig. 1. Then tube 18 is slipped over the spirals of tube14 (from the cold end) until threads 54 meet; then tube 18 is screwed ona sufficient distance to give the proper needle-valve setting, i.e.until needle 56 projects far enough into orifice 53. In the assembly,tube 14 is pushed a suitable distance into annular space 59 and may thenbe soldered or otherwise fixed in position relative to block 58, asindicated above.

The arrangement of the above-described refrigerator unit with a Dewarand a detector cell is shown in Fig. 4. Specifically illustrated is thedevice of Fig. 1, with outside tube 18, entrance conduit 20, skirt 36,pipe 40, and end 28 of tube 18. A Dewar 70 is provided, surrounding thecold end of tube 18 and the major part of the length thereof. This Dewarhas outer wall 71, inner wall 73, and evacuated space 75 therebetween,and is provided with a fluid-tight seal 72 against tube 18, andevacuated. A detector cell 74 is positioned adjacent the outer face ofend 28 with the end of inner Dewar wall 73 therebetween, and joined byleads 76 passing through seals 78 in the Dewar wall to a suitabledetecting, measuring, or other identifying device 80 which receives thesignal from cell 74. Opposite cell 74 is a window 82 in the Dewar wall,made of special glass or other material which permits passage of theradiation to be detected by cell 74.

The assembly shown in Fig. 4 is mounted in any desired fashion, so thatthe detector cell and its window will face the radiation to be detected.Device 80 may be located at a relatively remote distance and may receiveleads from several of these assemblies. Thus, in a fire detectingsystem, several of the units shown in Fig. 4

.may be mounted in several places with windows 82 facing variousstrategic spots, and all these units may feed into one detecting device80 which may be equipped with signal lights, alarm means, or otherwise,including indicia corresponding to the location of each detecting unit.

Any suitable arrangement for providing a supply of compressed gas to therefrigerating device of Figs. 1-'3 may be employed, such as that shownin Fig. 5. As there shown, compressor 90 compresses the gas (e.g. air ornitrogen) which is used for refrigeration; the heat of compression islargely removed from the gas in an aftercooler associated with thecompressor 90, in conventional fashion, and the cooled compressed gas isthen passed through appropriate purifying means such as oil separator 94and oil fume filter 96, to remove vas far as possible oils,hydrocarbons, and like impurities which if not thus removed wouldcondense in and block the passageways in the refrigerating device. Thecompressed purified gas then passes to the refrigerating device, hererepresented by the numeral 98, wherein its course is as described inconnection with Fig. 1. and after expansion therein passes through line99 back to compressor 90.

Gas holder 100, or other source of gas for refrigeration, is provided,with line 102 controlled by valve 104 leading into the system throughline 105. Original and make-up gas is supplied to the system by openingvalve 104. To avoid excessive pressure build-up in the system, e.g.,when the refrigeration requirements of unit 98 are relatively low, arelief valve 106 is provided leading from a point in the system, e.g.from separator 94, through line 108 back to compressor 90, connectingalso through line with surge tank 110.

' The devices hereinabove described are suitable for providing forexample liquid air or liquid nitrogen temperatures at the Vcold end ofthe refrigerating device. These are very effective for most detectingpurposes. However, even lower temperatures, such as those of liquidhydrogen, or even liquid helium, can be produced by providing aplurality of sets of channels for refrigerant gases.. A typicalarrangement for such purpose is shown in Fig. 6.

Four concentric channels, 110, 112, 114 and 116, are shown in Fig. 6.Channels 110, 112, and 116 are in the form of spiral threads, likethreads 12 of Fig. l, while channel 114 is formed with a spirally-woundstrip like strip 16 of Fig. l. At the inner end of each pair of channelsis a needle valve or equivalent expansion valve 118, 120. High pressurenitrogen or other refrigerant gas is admitted through a suitable opening122, Hows spirally-along the threads of channel 110, expands and coolsat needle valve 118, and returns through the threads of channel 112, incounter-current heat-exchange relation with inowing gas in channel 110,thereby cooling the latter. This expanded gas is then exhausted throughopening 124. High pressure hydrogen or other lowerboiling-point gas isadmitted through opening 126, flows spirally along the turns of passage114, expands and cools at needle valve 120, and returns through thethreads of channel 116, in counter-current heat-exchange relation withincoming gas in channel 114, thereby cooling the latter. The combinedcooling effect of the gas expansion in the outer channels 110 and 112with that in the inner channels 114 and 116 provides ultra-lowtemperatures of the device at the coldest region, i.e. around needlevalve 120.V Inasmuch as the temperature reached by the expandingnitrogen is higher than that of the other lowerboiling-point gas, thenitrogen passage does not extend the full length of the passage of theother gas, but stops short of the end thereof.

The arrangement of Fig. 6 may be modified if desired to provide that thenitrogen channels 110, 112 are on the inside and the longer channels114, 116 for the lowerboiling-point gas are on the outside.

Openings 122, 124, 126 and 128 of Fig. 6 are shown merelydiagrammatically; they may be connected in any suitable manner withlines leading to and from the compressors for the refrigerant gases. Aseparate compressor system, such as that shown in Fig. 5, is used foreach separate gas.

The Dewar 70 (Fig. 4) is fitted around the refrigerating unit shown inFig. 6 in the same way as illustrated in Fig. 4. The detector cell 74 isattached to the refrigerating Vunit adjacent the coldest region thereof,i.e. adjacent needle valve (Fig. 6).

In a typical arrangement as shown in Fig. 1, we may for exampleintroduce high-pressure gas at a rate of under 1.0 s.c.f.m. (say 0.4 to0.8 s.c.f.m.), and achievea cooling of the cold end to about 300 F. inabout 10 minutes. The system will run for several hours without pluggingof'thechannels, provided that an effective purification system for thegas isused. Plugging occurs 'more slowly as the rate of 'gasintroduction is lowered; thus, we have successfully operated the devicefor over 8 hours` with a fow rate of about 0.2 s.c.f.m. and an eflicientpurification system. When pluggingoccurs, the obstruction may be removedby bringing the heat exchanger Vunit up Yto room temperature and passingclean dry gas through it, preferably after opening the needle valve asby screwing entrance conduit 20 part way out of body member 30 (Fig. 1).

Various modifications in the apparatus of this invention, within thescope of the appended claims, will be evident to those skilled in thisart. For example, the various channels for high and low pressure gas maybe made either in screw-thread form (e.g. threads 12, Fig. l), or ofspirally edge-wound ribbon (eg. spirals 16, Fig. 1). The arrangementsshown in Figs. 1, 2, 3, and 6 are, however, the most convenient onesfrom the point of view of ease of manufacture and of assembly anddisassembly. Also, if it should be desired to use spiral strips insteadof screw threads for the inner channel of Fig. 2, the spirals would bewound further apart throughout the area there shown to be occupied bythreads 13.

We claim:

1. A refrigerating device comprising a heat exchanger including meansforming two concentric paths in heat exchange relation with each otheralong substantially their entire lengths, each of said paths being inthe form of a spiral passageway, entrance means at one end of said heatexchanger for introducing a gas at high pressure into the inner of saidtwo paths, exit means at said end for removing said gas, after theexpansion thereof, from the outer of said two paths, passage means atthe other end of said heat exchanger for leading said gas from saidinner path to said outer path, said passage means including an expansionvalve for expanding said gas, the spiral passageway of one of said pathsbeing movable longitudinally with respect to the spiral passageway ofthe other of said paths, and means cooperating with said pathformingmeans to elect such relative movement and thereby to regulate thesetting of said expansion valve.

2. A refrigerating device according to claim 1, further characterized inthat the spiral passageway of the inner of said two paths is of largercross-sectional area in its coldest region.

3. A refrigeration device having a heat exchanger assembly comprising acentrally disposed, externally spirally threaded rod, an innercylindrical heat-conductive tube tting against the apexes of the threadsof said rod and with said threads defining a first channel, aheat-conductive metallic strip spirally wound around and thermallybonded to said tube, an outer cylindrical tube closely surrounding saidstrip and with said strip defining a second channel; gas inlet means andgas outlet means positioned at one end of said heat exchanger assemblyand separated from each other by said inner tube, an expansion valvepositioned at the other end of said heat exchanger assembly andcomprising an orifice and a needle, said expansion valve providing anadjustable passageway between said channels whereby the flow of gasbetween said channels is controlled, said orifice communicating with,and in xed position with respect to, said iirst channel, said needlebeing in xed position with respect to said second channel, and means foreffecting relative movement between said lneedle and said orificewhereby to open or close the latter, said last-named means comprising athreaded member attached in xed position with respect to said outertube.

4. A refrigeration device according to claim 3, further characterized inthat said threaded member cooperates with a second threaded member whichis in xed position with respect to said gas outlet means.

5. A refrigeration device according to claim 3, further characterized inthat said rst channel is of larger crosssectional area adjacent saidother end of said heat exchanger.

6. A refrigeration device according to claim 3. further characterized inthat said heat exchanger assembly is in heat exchange relationthroughout a substantial portion of its length with a second heatexchanger, said latter exchanger comprising two spiral passagewaysarranged for countercurrent ow of a gaseous fluid and an expansion valveproviding a passage for and arranged to expand, and thereby cool, saidgaseous uid in passing from one of said spiral passageways to the other.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Article: Attenuated Superconductors, by Andrews et al.,published in Review of Scientific Instruments, vol. 13, July 1942, pages281-292.

